Light-emitting diode (LED) is a solid-state semiconductor light-emitting device, which is widely applied in luminous fields like indicator light and display screen.
At present, LED wafers are mainly produced via metal-organic chemical vapor deposition (MOCVD). The process is briefly introduced as below: put the substrate (today, mass-produced substrates mainly include sapphire substrate/Si substrate/SiC substrate) on the pocket profile of the graphite wafer carrier and transfer the substrate and the graphite wafer carrier to the MOCVD reaction chamber. Raise temperature of the reaction chamber to the set temperature, and feed meta-organic compound and Group V gas to break chemical bonds and rejoin a LED epitaxial layer on the substrate.
In the manufacturing process of LED epitaxial wafers, high-quality GaN material is often fabricated via heteroepitaxy. It is very important to choose the right type of substrate as different substrates would directly affect the lattice qualify of the grown epitaxial layer. Consider the following factors when selecting a substrate: lattice constant match, match of thermal expansion coefficient and appropriate price; in addition, different substrates also result in process difference from epitaxy to subsequent LED chip manufacturing process.
Today, substrates available for mass production mainly include sapphire substrates, Si substrates and SiC substrates. However, these substrates are not cost effective and difficult for mass production. Though numerous effort have been made to optimize epitaxial growth and subsequent manufacturing process of LEDs, the fall in LED cost still remains slow, which greatly prevents LEDs from popularization. Therefore, it needs to seek for a mature design of low-cost substrate and an epitaxial bottom structure for supporting the substrate growth.